I think PAF is getting food deals as Russia needs money and PAF needs plane to start protecting gawadar. I mean it'd take 5-10 years to get full fleet, so they've to plan now. Russia will get a needed deposit.
But I hope PAF thinks about future too. I think Russia is only su-35 operator whereas many nations use f-15. This means we can buy used ones from Saudi/other countries in future or parts. Also in future war with India, Russia will side India more than US will side India, we might not get engines etc etc because Russia makes some excuse. Perhaps they can do an agreement before.
Perhaps the Russian discount is just too good?